RESPIRATION

1. KEY STAGE 4 RESPIRATION

2. So far, we have considered both the structure of the breathing system and how it is adapted for breathing in and out. BUT... We have not talked about why the body needs to breathe. If you remember, we know that we breathe constantly throughout life. Also, we know that if we stopped breathing we would eventually die. So, breathing in Oxygen (O2) must be linked to something that we need constantly and without it our bodies would die. The answer is ENERGY making.

3. The energy making process depends on the breathing system and the digestive system. Imagine a fire... This will produce energy in the form of heat but only if it is supplied with 2 main ingredients. FUEL OXYGEN

4. Well, the bodies energy making reaction needs similar things to the energy making process of fire. Like the fire, the body needs Oxygen and a Fuel. And the fuel (in the form of digested food) comes courtesy of the digestive system The Oxygen is supplied by the breathing system + 2

5. If we now think back over the journey of oxygen and digested food through the human body, we will realise that they both end up in the same place. Food Oxygen Breathing system Digestive system These substances eventually arrive at the body cells BLOOD

6. Therefore, the raw materials for the energy making process eventually arrive at the body cells. capillary Blood + Oxygen Food muscle cell This energy making process is known as... R E S P I R A T I O N Each living cells is supplied with food and oxygen in order to generate energy.

7. No chemical reaction is 100% efficient. Therefore, as well as producing the useful energy, respiration also produces waste products. These waste products must be removed from the body If the process of breathing in is used to obtain the O2 for respiration, it would make sense for the body to use the process of breathing out to remove these waste products of this reaction. This is exactly what happens!!

8. Test One If we study the composition of the air that is breathed out, we will identify the waste products of respiration. Two tests help us identify these waste products. Before you start exhaling, the lime water is a clear liquid Blow gently through a straw into a test tube filled with lime water. After a short while, the lime water becomes cloudy. straw lime water

9. If a gas is bubbles through lime water and the liquid becomes cloudy, the gas is identified as…. Test Two Carbon Dioxide (CO2) This is the first of our waste products of respiration. On a freezing cold day, watch what happens when you breathe out. The air you breathe out is visible because the mystery waste product condenses back into a liquid.

10. This waste product is water vapour and so our final waste product of the process of respiration is... Water Using this information, we can now write out the full equation for respiration FOOD (GLUCOSE) + + + CARBON DIOXIDE OXYGEN WATER ENERGY from digestive system from breathing system waste product exhaled waste product exhaled USEFUL!

11. However, to call this reaction just ‘respiration’ is not quite correct. Let us try to understand why….. Think about what you do in an average day Sometimes you are resting Low energy requirements Sometimes you are active High energy requirements

12. Your body requires different amounts of energy at different times. The process of respiration must be able to ‘speed up’ and ‘slow down’ This is exactly what happens This will mean that we need different amounts of food to feed the reaction Therefore... Our rate of breathing will change The blood will have to flow at different speeds according to demand It will also mean that we need different amounts of oxygen to feed the reaction

13. 1. Sleeping 2. Running a marathon It seems that the process of respiration changes during the course of the day. Let’s take two extreme examples human activity and see how the process of respiration change... This may not represent the daily activities of an average human, but this scenario will help us understand this process of respiration in more depth.

14. What happens to the process of respiration when the body is performing these different activities. Let’s deal with each one in turn. SLEEPING When we sleep, our body is at rest. There is a low demand for energy. Low demand for food and oxygen Blood flow does not have to be rapid Low energy demand The breathing rate remains normal In other words, the body has plenty of time to inhale the oxygen that it needs. It also has time to completely digest the food to release the important chemicals (e.g glucose). The blood can efficiently transport these substances to the cells without increasing its rate of flow.

15. When the body is performing respiration in such as way, it is given a special name. When the body… O2 • has plenty of oxygen • is able to completely digest food • can supply the cells with the oxygen and food that they need We say it is performing AEROBIC respiration.

16. So our original equation for the process of respiration is actually the equation for aerobic respiration. Glucose + Oxygen Carbon Dioxide + Water + Energy This is an efficientprocess... Our bodies perform aerobic respiration for much of the day. In fact, as long as the supply of Oxygen remains high enough, we will continue to perform aerobic respiration. Enough energy is made to supply the whole body Of course, the amount of energy we produce will drop if the level of oxygen drops.

17. before during So, now we know that there is a form of respiration which is performed when there is a supply of oxygen to the body. But, what happens in situation 2? remember the runners? Are they performing aerobic respiration? Well, in order to answer that question, we have to think about what their bodies are doing during the race. after

18. What’s happening? Energy Demands Oxygen available Form or respiration Low High Aerobic before Aerobic (but slowing) High Low / None during Dropping None / Low ? after

19. How can the body perform aerobic respiration in this situation? ? Aerobic respiration requires oxygen but when you have been running a race or doing strenuous exercise, you cannot inhale enough oxygen for this reaction. Glucose + Oxygen Carbon Dioxide + Water + Energy This process fails! But, if this process fails when the oxygen levels drop, the body would be left with absolutely no energy.

20. No energy would lead to stop working! ? ? ? ? The problem is that we often do exercise and our bodies continue working. This would mean that the body would stop working whenever it became short of oxygen. ? ? ? The body must be able to keep working through short periods of low/no oxygen. What must be happening when our oxygen levels drop to zero? ? ? HOW?

21. Well, it is quite a remarkable process….let’s examine it. With aerobic respiration, the cells supply of oxygen and food is relatively constant When this supply is cut off, the cell is left with excess food and lacks energy. Oxygen Food blood cell It solves this problem by making energy from just the food alone!

22. Now because it is releasing energy from food, it is still performing respiration. But... It is not aerobic respiration because there is no oxygen present. (aero- means of air) Therefore we call it ANAEROBIC respiration The energy being made by breaking down the food without oxygen. This seems a better process! To be able to make energy without needing oxygen would be very beneficial. However, there is a problem.

23. Remember the last time you ran a race, carried a heavy weight or swam under water for too long and ran short of breath. It probably felt uncomfortable. Well, if anaerobic respiration was as efficient as it sounds, this lack of comfort would not happen. So, what is the problem with anaerobic respiration? When the cell breaks down the food to release the energy, it also makes a potentially harmful waste product. The breakdown of the food is also incomplete. It is not an efficient process.

24. Glucose Lactic Acid + (some) Energy This waste product is known as LACTIC ACID. Therefore the equation for Anaerobic respiration is… waste product not as much energy as with aerobic respiration from the digestive system You will notice that this reaction is only an option for short periods of time. This is because the waste product is harmful and not enough energy is made to satisfy the body.

25. Why is Lactic Acid so harmful? Well, this chemical can stop muscles within the body, from contracting and relaxing. Relaxation The Lactic acid soaks the muscle cells and prevents the muscle cell from doing its job. Contraction If the muscles in your body stop contracting and relaxing they are said to be fatigued. They eventually seize and you experience cramp.

26. If you want to consider the full impact of damage caused by the presence of Lactic Acid, just remember that the heart is made of muscle cells! This leaves us with a problem... If we want to do exercise YES NO We want the energy that anaerobic respiration produces But we don’t want the Lactic Acid waste product So the answer is for anaerobic respiration to be a ‘gap-fill’ during periods of very low / no oxygen availability.

27. In other words…. rest exercise stops Aerobic Anaerobic exercise oxygen levels time Anaerobic respiration keeps our bodies going until we can breathe in more oxygen again. Whilst we are performing anaerobic respiration, our bodies are building up a ‘debt’ of oxygen.

28. This is rather like owing the bank some money. Once you get some money, you have to pay off that debt. We can think of that debt as being the presence of lactic acid in the body. When our bodies convert from aerobic to anaerobic respiration, we start making lactic acid. As soon as this begins, the body starts building an oxygen debt. This is equivalent to the amount of oxygen it would have used if aerobic respiration had continued.

29. This oxygen debt will have to be repaid when the exercise stops. Oxygen will be used to break down the lactic acid that is present in the body. The oxygen ‘oxidises’ the lactic acid. In fact, the lactic acid is oxidised into carbon dioxide and water. In this way, the process of aerobic respiration can be converted into The process of anaerobic respiration which can then turn back into...

30. Glucose Glucose Glucose + + Oxygen Oxygen Carbon Dioxide Carbon Dioxide + + Lactic Acid water water + + + Lots of energy little energy Lots of energy before exercise after exercise at rest again

31. Glucose + Oxygen Carbon Dioxide + Water + Energy So, in summary, the body has the ability to produce energy, despite changes in the supply of oxygen. Here are the two forms of respiration. Aerobic respiration(complete breakdown of food) oxidised Anaerobic respiration(incomplete breakdown of food) Lactic Acid + Little Energy Aerobic respiration is performed when oxygen is present Anaerobic respiration is performed when oxygen is absent

32. Now that we know how the energy is made, we need to consider what it is used for? Remember, cellular respiration occurs all over the body. Energy Therefore this energy is used for the many processes that sustain life. Amongst all these, there are a few important uses that we can examine.

33. What is energy used for? 1 To allow muscles to contract 2 To build up large molecules from smaller ones 3 To help maintain a steady body temperature 4 To power the active transport of substances within the body

34. We can consider each one in turn. 1 To allow muscles to contract and relax. In order for muscles to have an effect, they must move something in the body. Often this tends to be a bone.

35. muscle By moving the bone, they create a lever which does some work. bone Using energy generated within the muscle, it contracts and alters the position of the bones. In doing so, work can be done e.g. something can be lifted. Muscle contracted Muscle relaxed energy

36. 2 To build up large molecules from smaller ones. In order for the human body to stay healthy, it must obtain nutrients from the 7 food groups. These are: Fats Minerals Water Fibre Proteins Vitamins Carbohydrates A balanced diet should contain elements from all 7 groups.

37. Once we have digested the food from our diet, we release many useful substances. DIET Respiration digestion Useful raw materials ENERGY The body uses the energy from respiration to turn these raw materials into useful substances.

38. A simple example of this use of energy can be seen when the body builds new proteins from amino acids. Step 1 Proteins are eaten as part of our food (e.g. protein in eggs) Step 2 These proteins are made of amino acid chains. The order of the amino acids is specific to the protein. amino acids

39. Step 3 This protein may not be the one that the body requires. Therefore, the digestive system uses protease enzymes to break up the amino acid chain. Step 4 This process of digestion releases the individual amino acids.

40. Step 5 Now that the raw materials are free, the body then uses the energy from respiration to assemble them into new proteins. A new protein will have a different order of amino acids. Energy new protein (old) respiration

41. Step 6 This new protein, and others like it, will now be used in different ways by the body. The energy from respiration has made this possible.

42. 3 To help maintain a steady body temperature. The conditions outside our body are constantly changing. One minute they can be hot, the next cold. Despite this, our bodies must be kept at a constant temperature.

43. This constant temperature is 37oC. The reason why our bodies must remain at 37oC is because this is the temperature at which enzymes work most effectively. You may remember that enzymes are chemicals that control many of the chemical reactions within our bodies. Therefore... colder hotter 37oC Enzymes working slowly and the body is suffering. Enzymes working well and body is fine. Enzymes damaged and body can become ill.

44. The temperature of the body is controlled by a region of the brain. As blood flows around the body, it also visits this ‘thermo-regulatory’ centre in the brain. The brain senses the bodies temperature by sensing the temperature of blood. REST OF BODY Once it knows what the body temperature is, it can act accordingly. In order to understand what happens, think about what your body does when it is hot or cold outside. How do you react?

45. On a hot day… Remember that blood flows through vessels which are lined with muscle cells. blood artery outer wall You sweat. Blood is pumped to the surface of your skin. If we consider the second of these effects, we can see where the energy from respiration is used.

46. These muscle cells contract and relax using energy fromrespiration. The contraction and relaxation of these muscles can affect the blood flow through the vessel. E.g. if the muscle runs in a circular direction around the vessel, when it contracts, it could constrict the blood flow If a blood vessel is constricted in this way, blood flow is reduced and this in turn, will affect the direction of blood flow through the body. The opposite is also true. If the muscles relax, the blood vessel could become wider and the blood flow increases.

47. skin Blood vessels Now, if we consider the blood vessels within the skin, we see how the contraction and relaxation of blood vessel muscles affects the flow of blood. surface of the skin Direction of blood flow We can see that blood can flow in different directions within the skin. When the brain senses that the body is too hot, it takes steps to redirect the blood flow to the skin surface.

48. The brain can cause the contraction and relaxation of muscles within the walls of these blood vessels. Energy from respiration is used to power the contraction of these muscle cells. Brain BLOOD makes the blood flow to the surface of the skin > 37oC this vessel widens this vessel constricts

49. When the blood flows to the surface, it comes into close contact with the air surrounding the body. This air is much cooler than the temperature of the blood. HEAT HEAT HEAT air skin blood The heat within the blood escapes to the cool air and the result is that the body’s temperature drops. Remember, respiration produces the energy that is needed by the muscle cells within the walls of the blood vessels.

50. 4 To power the active transport of substances within the body. This is our final use of the energy generated during respiration. In order to understand how active transport works, we must firstly consider the concept of diffusion. Diffusion is the movement of a substance from an area of high concentration to an area of low concentration.